Process for curing pneumatic tires

ABSTRACT

A method for curing already toroidally shaped pneumatic tires. The tire beads are forced into their respective seats in axially approachable mold section while the mold sections are spaced from each other and the mold open. A flexible curing bag is introduced inside the tire, expanded, and pumped to remove air trapped between its outer surface and the inside of the tire while the beads remain in their respective seats. The mold is then closed and the tire cured. Rigid mechanical means can be used to force the beads into the seats.

United States Patent Caretta et al.

[ July4, 1972 PROCESS FOR CURING PNEUMATIC TIRES Inventors: RenatoCaretta, Gallarate; Antonio Pacciarini, Milan, both of Italy Assignee:Industrie Pirelli S.p.A., Milan, Italy Filed: Jan. 13, 1970 Appl. No.:2,510

Related US. Application Data Division of Ser. No. 607,227, Jan. 4, 1967,Pat. No. 3,520,024.

Foreign Application Priority Data Jan. 13, 1966 Italy ..l3350/66 [56]References Cited UNITED STATES PATENTS 3,378,882 4/1968 Turk et al..l8/2 TP 2,741,799 4/1956 Heston 3,153,263 10/1964 Mallory et al..l8/l7 W Primary ExaminerRobert F. White Assistant Examiner-J. I-I.Silbaugh Attorney-Stevens, Davis, Miller & Mosher [5 7] ABSTRACT Amethod for curing already toroidally shaped pneumatic tires. The tirebeads are forced into their respective seats in axially approachablemold section while the mold sections are spaced from each other and themold open. A flexible curing bag is introduced inside the tire,expanded, and pumped to remove air trapped between its outer surface andthe inside of the tire while the beads remain in their respective seats.The mold is then closed and the tire cured. Rigid mechanical means canbe used to force the beads into the seats.

4 Claims, 24 Drawing Figures PATENTEDJUL 41912 3,674,899

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' INVENTOBS RENATO CAR ETTA ANTONIQ PACCIARINI Stevens, Davis, Miller 81Mosher ATTORNEYS P'A'TE'N'TEDJUL "4 I972 SHEET 8 OF 9 Fig. I914INVENTORS RE| |ATO CARETTA ANTONIO PACCIARINI Stevens, Davis, Miller &Mosher ATTORNEYS PROCESS FOR CURING PNEUMATIC TIRES This application isa division of application, Ser. No. 607,227, filed Jan. 4, 1967, now US.Pat. No. 3,520,024.

BACKGROUND OF THE INVENTION 1 Field of the Invention The presentinvention relates to a method for curing pneumatic tires or of similarhollow articles provided with reinforced edges, and, more particularly,to such a method utilizing a flexible curing bag inserted in the hollowarticle.

2. Description of the Prior Art As it is known to the techniciansskilled in the an, a curing bag is introduced into the pneumatic tire tobe cured in order that heating fluid can be circulated through the bagto cure the tire. However, in these known arrangements, the curing bagis unable to adhere completely to the inner surface of the tire, sinceair pockets are formed between said surface and the outer surface of thecuring bag itself. In fact, the curing bag, when introduced in the tire,adheres at first in a tight manner to the edges constituting the tirebeads; then, by virtue of the admission of fluid under pressure in itsinside, the bag expands and tends to adhere to the mid-circumferentialportion of the tire, so that the air trapped between the tire and thecuring bag accumulates into pockets which are located between themidcircumferential portion and the beads of the tire. The air trapped insaid pockets is subjected to a temperature rise during the curingoperation and consequently tends to expand and to penetrate between thecarcass plies, thus causing bubbles and detachments of the plies,resulting in a faulty cured tire.

In order to try to avoid the harmful consequences due to air occlusionsbetween the outer surface of the curing bag and the inner surface of thetire, curing bags have been adopted which are provided on their outersurface with a knurl or with a net of grooves intended to facilitate thedischarge of the trapped air, which is then able to escapethrough theclearances existing between the mold sections.

This solution, however, does not ensure satisfactory results since thegrooves obtained on the outer surface of the curing bag are very likelyto get obstructed, and the curing bag is weakened on account of thereduction in its thickness at said grooves. In addition, the pattern ofthe outer surface of the curing bag remains permanently molded insidethe tire during the curing operation so that the inner surface of thelatter becomes irregular. Therefore, in order to create vents for theair trapped in the pockets, some holes are often made by hand, with atool, by the curing operator in proximity of the tire beads. Such holesare automatically closed during the curing operation, but, in additionto resulting in a considerable loss of time, the perforation of the tireoften involves the cut of some reinforcing cords of the carcass plieswhich results in a reduction in the resistance of the carcass to thestresses to which it is subjected during service.

A further serious drawback which usually takes place during theintroduction of the tire in the curing unit is due to the imperfectpositioning of the tire in the mold, especially due to the fact that itsbeads come in contact with the corresponding seats provided in the mold,but do not completely penetrate into them. The beads are thereforesubjected to subsequent displacements and rotations, also due to theweight of the tire itself. In this case a tire is obtained, in which thetread and the possible reinforcing annular structure are not perfectlycentered, which irregularity has a dangerous effect on the behavior ofthe tire under service.

SUMMARY OF THE INVENTION The object of the present invention is toprovide a method which eliminates the above-indicated drawbacks, andwhich, in general, includes the steps of bringing the reinforced edgesof the article to be molded into contact with a corresponding seatprovided in a first and second mold section, respectively, forcing saidedges into their corresponding seats, introducing a curing bag insidethearticle by admitting compressed fluid inside said curing bag,exerting a pumping action on the air trapped between the curing bag andthe inside of the article at at least one of the portions limiting thereinforced edges of the article, closing the mold, and subjecting thearticle to the curing treatment.

This and other features of the present invention will be more clearlyapparent from the following description of an embodiment of the same,illustrated by way of example in the attached drawings, in two curingunits of the type described in applicants US. Pat. No. 3,337,918.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 8 are vertical sectionalviews, representing the subsequent steps of the above-indicated process,carried out on a curing unit incorporating a curing bag and providedwith a mold comprising a lower section and an upper section, bothannular and continuous, and an intermediate section constituted byradially displaceable sectors;

FIGS. 9 and 9a are vertical sectional views, representing the apparatusprovided in the curing unit shown in the preceding figures for forcingthe tire beads in their respective seats, the apparatus being shown inthe rest position in FIG. 9 and in the operative position in FIG. 9a;

FIGS. 10 and 10a are horizontal sectional views, representing theapparatus provided in the curing unit shown in the preceding figures forforcing the tire beads in their respective seats, the apparatus beingshown in the rest position in FIG. 10 and in the operative position inFIG. 10a;

FIGS. 11 to 18 are vertical sectional views, representing the subsequentsteps of the process carried out on a curing unit incorporating a curingbag, of a type different from that represented in the preceding figures,but also provided with a three-section mold; and

FIGS. 19, 19a, 20 and 20a are views similar to FIGS. 9, 9a, 10 and 10a,respectively, and represent the device provided in the curing unit shownin FIGS. 11 to 18 for forcing the tire beads into their respectiveseats.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring specifically to FIGS.1 to 8 of the drawings, the reference numeral 1 refers to an alreadygenerally toroidally shaped pneumatic tire carried by a curing unitprovided with a mold divided into three sections, namely a lower section2 and an upper section 3, both annular and continuous, and anintermediate section including a plurality of annular sectors 4 whichcan be displaced either centripetally or centrifugally with respect tothe axis of the curing unit.

As shown in FIG. 2, the lower section 2 is secured to the outer surfaceof a plate 5 integral with the base 6 of the curing unit. Temperatureconditioning fluid is circulated within recesses 7 fonned in plate 5,said fluid being admitted and discharged through suitable ducts 8. Theupper section 3 is secured to the lower surface of a plate 9 housedinside the lid of the curing unit and provided with recesses 10, withinwhich temperature conditioning fluid is circulated, said fluid beingadmitted and discharged through suitable ducts 11. The intermediatesection consists of a plurality of annular sectors 4, each of which issupported by a corresponding support 12. Inclined planes 13, sliding onguides 14, are provided for the displacement of said sectors 4, thenumber of the planes being equal to that of the corresponding sectorsand supports.

The guides 14 are integral with the sides 15 of the base 6, sides 15being provided with recesses 16 within which temperature conditioningfluid is circulated, said fluid being admitted and discharged throughducts similar to the preceding ones, but not shown in the figures.

As shown in FIG. 3, the central part of the base 6 contains acylindrical container 17 adapted to slide in a vertical direction, andwithin which is disposed, in rest position, a flexible bag 18. This baggenerally has a toroidal shape and its edge 19 is clamped between theedge 20 of the container 17 and a ring 21 integral therewith.

A cylinder 22 is assembled inside the lid of the curing unit, saidcylinder being coaxial with the plate 9, and containing a hollowcylinder 23 which, in turn, contains a stem 24. Cylinder 23 and stem 24are slidable together or separately within the cylinder 22 by means ofsuitable controlling devices not represented in the figure.

At its lower end, the cylinder 23 terminates with a bellshaped enlargedcrown 25, in which are assembled the mechanical means for forcing thebeads of the tire into the corresponding seats obtained in the rings 26and 27 of the lower and upper half molds, respectively.

With reference to FIGS. 9, 9a, and 10a, the means for forcing the beadsinto their seats comprise a plurality of sectors 28 which, through pins29, are supported by the crown 25. Each of the sectors 28 is providedwith an extension 30, on which is pivoted a small wheel 31. Alsoprovided in each sector 28 is a recess 32, in which is inserted acylindrical helical spring 33 wound about a pin 34 radially disposedinside the crown 25. A blade-shaped extension 35 extends from eachsector 28.

The stem 24 is hollow and has a cylinder 36 extending therein. At thelower end of cylinder 36 is screwed a core 37, formed by two cylindricalportions having different diameters and connected by a frusto-conicalportion. A hemispherical cap 38 is secured at the lower end of the core37.

The steps of the method of the present invention are generallyrepresented by FIGS. 1 to 8. As shown in FIG. 1, the curing unit iscompletely opened and the tire I is disposed on the lower section 2 ofthe mold, with its lower bead lying on the ring 26.

As shown in FIG. 2, the lid of the curing unit is then lowered until thering 27 of the upper section 3 of the mold comes into contact with theupper bead of the tire. At the same time the stem 24 is lowered furtherto the proximity of lower ring 26 and, as shown in the right half ofFIGS. 9 and 10, the core 37 is also lowered by sliding within the stem24. Consequently, the sectors 28 are centrifugally pushed by virtue ofthe rolling of the small wheels 31 along the frusto-conical surface ofthe core 37, while the springs 33 are compressed. At the end of themovement of sectors 28 towards ring 26, the extensions 35 protrudebeyond ring 26 and force the lower bead of the tire into thecorresponding seat provided on ring 26 so as to ensure a correctpositioning and an efficient fastening of the tire.

As shown in FIG. 3, the upper bead is then forced into its correspondingseat provided on the ring 27. For this purpose the stem 24 is caused toslide upward together with the cylindn'cal body 23 and crown 25 to theposition as shown in order that the mechanical forcing devices may forcethe upper bead of the tire into its corresponding seat in the same wayas described above in respect to the lower bead. After this has beenachieved, the sectors 28 are centripetally displaced by operating, in anopposite sense to that indicated above, the devices assembled in thecrown 25, the hollow stem 24 thus being caused to slide upward withinthe cylindrical body 23.

The tire 1 is now fixedly secured to the lower and upper sections of themold and, as shown in FIG. 4, the curing bag 18 is inserted within saidtire by admitting fluid under pressure in the lower part of thecontainer 17.

The curing bag 18, owing to the action of the fluid under pressure, ispushed outside the container 17, penetrates into the tire, and adheresinitially to the mid-circumferential band of the tire, and progressivelyto positions nearer and nearer to the beads. In this way air pockets Sare formed between the outer surface of the curing bag and the innersurface of the tire, in proximity of the beads.

FIGS. 5 and 6 represent the method for eliminating the air trapped inthe pockets S. The stem 24 is pushed downward together with thecylindrical body 23, while the container 17 is pushed upward so that thecuring bag 18, whose edge 19 is clamped between the edge of thecontainer 17 and the ring 21, is thus forced to contract, this movementbeing further aided by the downward movement of hemispherical cap 38 onstem 24, and by the surface formed by sectors 28. In this manner thecuring bag 18 adheres to the inner surface of the tire only along amid-circumferential band of the latter.

It is to be understood that the pumping action, consisting ofcontracting and expanding the curing bag, can be carried out onlypartially, namely by displacing only the container 17 without causingthe stem 24 to slide, in which case the curing bag 18 detaches only inits lower part from the inner surface of the tire I, or vice versa.

The following step of the cycle, represented in FIG. 6, concerns there-expansion of the curing bag 18 which causes the complete expulsion ofair between it and the tire, thus allowing the curing bag to adhereprogressively to the whole inner surface of the tire, starting from theabove-cited mid-circumferential band. Air so expelled is completelydischarged through the clearances of the mechanical parts constitutingthe curing unit as indicated by the arrows in FIG. 6.

FIG. 7 depicts the manner in which the curing bag 18 adheres perfectlyto the inner surface of the tire I at the end of the above operation.

FIG. 8 shows the final position taken by the upper section 3 of the moldfor the curing operation after a subsequent partial lowering of the lidof the curing unit.

The complete lowering of the lid causes the centripetal displacement ofthe sectors 4 constituting the intermediate section of the mold, andtherefore, the total closure of the curing unit, as more specificallydisclosed in the cited US Pat. No. 3,337,918.

During the various steps of the operating cycle the tire 1 remainsfimtly secured, since its beads have been initially forced in thesuitable seats provided on the rings 26 and 27 of the lower sector 2 andof the upper sector 3, respectively, of the mold.

FIGS. 11 to 18 represent the steps of the method carried out on a curingunit different from that described in the preceding embodiment. Asindicated in FIG. 11, this second curing unit comprises a flexiblecuring bag 40 assembled with vertical axes, which in the rest positiontakes a cylindrical shape. The inner edge 41 of this curing bag isclamped between a disk 42 and a ring 43, and the outer edge 44 of saidcuring bag is likewise clamped between a disk 45 and a ring 46. The disk42 is assembled on a vertical stem 47 by means of a sleeve 48, stem 47being axially slidable within the sleeve 48, while disk 45 is keyed onthe stem 47.

FIGS. 19, 19a, 20 and 20a depict the apparatus for forcing the beads ofthe tire into the suitable seats obtained in the mold sections accordingto the embodiment of FIGS. 11 to 18.

This apparatus is disposed below the disk 42 and comprises a pluralityof sectors 49 pivoted on the lower surface of said disk and adapted torotate about the fixed pins 50. Each sector 49 is provided with agrooved guide 51 within which is inserted a pin 52 secured on the uppercrown 53 of a cylinder 54 which is encased in the base of the curingunit, is coaxial with the stem 47, is adapted to rotate about its ownaxis, and is displaceable in a vertical direction.

In FIGS. 19 and 20 the sectors 49 are represented in rest position,while in FIGS. 19a and 20a they are represented in their expandedposition for forcing the bead of the tire into its corresponding seat.The latter position is achieved after the rotation of the crown 53 in acounterclockwise direction has caused the rotation of the sectors 49about the pins 50 due to the action of pins 52 in the guides 51, so asto displace said sectors centrifugally. To bring the sectors from theexpanded position to the rest position, the operation is carried out byrotating the crown 53 in a clockwise direction.

FIGS. 11 to 18 represent the steps of the process forming the object ofthe invention, which are the same described with reference to FIGS. 1 to8.

FIG. 11 represents the tire after it has been inserted on the curing bag40, the latter having a cylindrical shape since the disks 42 and 45 towhich its edges are fixed have been brought to the greatest possibleaxial distance from each other, the tire being positioned with its lowerbead lying on the ring 57 of the lower section 58 of the mold.

Then, as shown in FIG. 12, the lid 56 of the curing unit, to which theupper section 59 of the mold is fixed, is lowered until the upper headof the tire comes in contact with the corresponding seat 55 provided insection 59. To force the upper bead in its seat, the cylinder 54 ispushed upward and the sectors 49 are expanded by rotating the cylinder54 about its own axis.

Subsequently, as shown in FIG. 13, the cylinder 54 is again pusheddownward together with the curing bag 40 connected to it, and thesectors 49, maintained in their expanded position, force the lower headof the tire in the seat formed on the ring 57 of the lower section 58 ofthe mold.

To insert the curing bag 40 in the tire, after having brought thesectors 49 to their rest position, the stem 47 is caused to slide withinthe sleeve 48 as illustrated in FIG. 14, so that the disk 45 approachesdisk 42, after which compressed fluid is admitted inside the curing bag40 through an opening not shown in the FIGS.

It has been discovered that air initially filling the tire is unable toescape completely, causing air pockets S to form between the outersurface of the curing bag and the inner surface of the tire. Toeliminate these pockets, the stem 47 is caused to slide downward and thecylinder 54 upward, as shown in FIG. 15, so as to cause mutual approachof disks 42 and 45 to which the edges of the curing bag 40 are clamped.

The curing bag is therefore compelled to contract and remains adherentto the inner surface of the tire only along a mid-circumferential bandthereof. The stem 47 and the cylinder 54 are then mutually displaced, asshown in FIG. 14, by raising stem 47 and lowering cylinder 54 so as tocause the curing bag 40 to adhere again progressively to the innersurface of the tire, starting from said mid-circumferential band. Inthis way it is possible to eliminate the air trapped in the pocketswhich, following the path indicated by the arrows, passes through theclearances existing between the mechanical parts constituting the curingunit. It is to be understood that the pumping action, consisting ofcontracting and expanding the curing bag, can be carried out onlypartially, when sufficient, by displacing only one of the disks 42 or45, the other of which is kept stationary.

The curing bag 40 is thus caused to adhere completely, as shown in FIG.17, to the inner surface of the tire, which, having its two beads firmlysecured in the suitable seats provided in the lower section 58 and theupper section 59 of the mold, remains correctly positioned during thewhole cycle.

The mold is then closed, as shown in FIG. 18, by further lowering thelid 56 of the curing unit, to which the upper section 59 of the mold isfixed. The lowering of the lid 56 causes the lowering of the disk 45which is integral with the stem 47. The latter thus slides within thesleeve 48 and causes the centripetal displacement of the sectors 60 ofthe intermediate section of the mold, in the manner disclosed in US.Pat. No. 3,337,918.

It is understood that the process forming the object of the presentinvention can be carried out with different means without falling out ofthe scope of the invention itself. For example, it can be carried out bymeans of a curing unit provided with a mold constituted only by twoannular continuous sections.

In conclusion, the main advantage of the present invention consists inthe complete elimination of the air trapped between the outer surface ofthe curing bag and the inner surface of the tire during the curingprocess, which is effected with a simpler, more rapid and more efficientmethod with respect to those adapted in the art up to the present time.

In achieving the above, it is necessary, not only to position the tirebeads in the corresponding seats provided in the mold of the curingunit, but also to force the beads in said seats, since it is absolutelynecessary for the tire to be firmly secured during this treatment andduring curing of the tire. Thus the anchoring apparatus of the presentinvention is obviously very advantageous since possible deformations anddisplacements of the tire elements are prevented.

Of course, variations of the specific construction and ar' rangement ofthis type mechanism herein disclosed can be made by those skilled in theart without departing from the invention as defined in the appendedclaims.

We claim:

1. A method for curing hollow, already generally toroidally shapedrubber tires which include two beads, comprising:

a. forcing the tire beads of the tire into respective seats of twoseparate axially approachable mold sections while maintaining said moldsections axially spaced apart from each other whereby the mold is inopen condition;

. introducing a flexible curing bag into the tire and expanding said bagby admitting compressed fluid thereinto whereby said bag substantiallycompletely fills the interior of said tire;

c. contracting and re-expanding said bag by displacing a radially innerportion thereof axially towards and then away from themid-circumferential plane of the tire in a manner whereby an outermostradial portion of said bag remains in outwardly pressing contact withthe inner wall of said tire along its mid-circumferential plane withoutdisplacing therefrom said beads from said seats during said contractingand re-expanding; and then d. closing the mold by axially approachingsaid mold sections towards each other and curing the tire within theclosed mold.

2. The method of claim 1, wherein the tire beads are forced into saidseats by rigid mechanical means.

3. The method of claim 1, wherein said contracting is carried out bysimultaneously displacing a radially inner part of both axially opposedradial walls of said bag towards each other whereby said bag peels awayfrom the inner wall of said tire progressively from the beads thereofand in the direction towards the tire mid-circumferential plane, andsaid re-expanding is carried out by permitting said walls to moveaxially apart from each other whereby said bag progressively expandsagainst the tire inner wall in the direction from themid-circumferential plane towards said beads.

4. The method of claim 1, wherein heated fluid is admitted to said bagand circulated through jackets in said mold sections to effect curing ofsaid tire.

2. The method of claim 1, wherein the tire beads are forced into saidseats by rigid mechanical means.
 3. The method of claim 1, wherein saidcontracting is carried out by simultaneously displacing a radially innerpart of both axially opposed radial walls of said bag towards each otherwhereby said bag peels away from the inner wall of said tireprogressively from the beads thereof and in the direction towards thetire mid-circumferential plane, and said re-expanding is carried out bypermitting said walls to move axially apart from each other whereby saidbag progressiveLy expands against the tire inner wall in the directionfrom the mid-circumferential plane towards said beads.
 4. The method ofclaim 1, wherein heated fluid is admitted to said bag and circulatedthrough jackets in said mold sections to effect curing of said tire.